1. Field of the Invention
This invention pertains generally to micromechanical resonators, and more particularly to a micromechanical resonator with a hollow attachment stem.
2. Description of Related Art
Capacitively transduced vibrating polysilicon micromechanical resonators have achieved Q's over 160,000 at 61 MHz and Q's larger than 14,000 at approximately 1.5 GHz, and most recently above 40,000 at 3 GHz. These high Q values make these micromechanical resonators particularly well-suited for on-chip frequency selecting and setting elements for filters and oscillators, such as utilized in wireless communication applications. The aforementioned Q's were achieved by first recognizing that anchor loss dominated at UHF, and using design strategies to suppress such loss, including attaching to the vibrating structure at nodal locations, minimizing support dimensions (e.g., reducing stem size), using different materials for the support and vibrating structure to effect an energy reflecting impedance mismatch, and using quarter wavelength supports. To date, oscillators employing the above high-Q resonators have already been demonstrated with phase noise performance commensurate with GSM cellular phone specifications for reference oscillators.
However, certain applications such as software-defined cognitive radio, demand even higher Q's at RF frequencies to enable low-loss selection of single channels (rather than bands of them) to reduce power consumption of succeeding electronic stages down to levels more appropriate for battery-powered handhelds.